The principal objective of this research is to characterize the phospholipase A2 (PLA2) in platelet membranes. This enzyme is responsible for the hydrolysis of fatty acids found in the number two position of platelet phospholipids. Arachidonic acid, a major constituent of the hydrolysis products, is a precursor of endoperoxides, prostaglandins, thromboxanes and prostacyclin--all of which are deemed to be of physiological significance in the thrombotic, hemostatic and coagulation processes. The effect of chemical modification of the membrane protein reactive side chains and of the phospholipid amines on platelet membrane phospholipase A2 activity is being investigated. Thus, the probing in situ of the biochemical properties of the active site of this enzyme will help to elucidate its mechanism of action. Furthermore, since the enzyme is a membrane-bound protein, and such proteins appear to be important for platelet function, we anticipate that these studies will provide new information and techniques in this important area of membrane research.